Sensors are well known in the art. When formed in a semiconductor material such as silicon or germanium such sensors may be provided as mechanical structures, for example as a MEMS arrangement, or electromagnetic (EM) radiation sensors such as infra-red (IR) sensors. By using materials such as silicon it is possible to form the sensor in one or more layers of the wafer from etching and other semiconductor processing techniques so as to result in a desired configuration. Due to the delicate nature of the sensors and their sensitivity to the surrounding environment it is known to provide a protective cap over the sensor, the cap serving to isolate the environment of the sensor from the ambient environment where the sensor is operable. Within the area of EM sensors there is a specific need for sensors that can be provided in a packaged form.